Generally, solar cell apparatuses are roughly divided into apparatuses of a so-called flat plate type where natural light from the sun is directly impinged on an element to generate electric power and apparatuses of a so-called light condensing type where natural light is condensed using an optical system to increase a luminous flux density or illuminance (luminous intensity) (hereinafter, collectively simply referred to as “luminous flux density”) and is then impinged on an element to generate electric power.
There are widely used schemes of the condensing type solar cell apparatuses such as a lens scheme in which light is condensed using lenses such as a circular Fresnel lens (focus scheme), a reflector scheme in which light is condensed using a parabolic mirror or side mirror and a scheme combining these two schemes. Furthermore, a light absorption/light emission scheme is also known whereby sunlight is absorbed by a light absorber/illuminant containing inorganic ions or organic dye without using any optical system and the light emitted from the light absorber/illuminant is introduced into an element (e.g., see Non-Patent Document 1).
Non-Patent Document 1: Japanese Patent Office homepage http://wwwjpo.go.jp/shiryou/s_sonota/map/kagaku04/1/1-3-5.htm “Solar Cell, 1.3.5 Condensing Type Solar Cell” (as of Jan. 20, 2009)